SECT. 4] 



BIOLOGICAL SPECIES, WATER-MASSES AND CURRENTS 



411 



unlike inanimate drift bottles, may exercise some degree of modification of 

 their distribution. This could be accomplished mainly by swimming from one 

 depth level to another during vertical diurnal migrations, or even through 

 seasonal migrations of this type. During these shifts of level, which occur under 

 the directive stimulus of light, even weakly swimming animals may con- 

 ceivably spend a good deal of time alternately in currents flowing in different 

 directions, or at different speeds. In this way a retardation or prevention of 



Fig. 13. Summary of the distribution of the Stage I, Stage VI and Stage XI (last) phyl- 

 losoma larvae of the spiny lobster Panulirus interruptus based on approximately 

 monthly cruises, 1949-1955. Superimposed on the grid is the surface-current pattern 

 for Aug. 21-Sept. 9, 1954. There is considerable variation in currents from month to 

 month but the general flow is to the south. August and September are months with 

 many earlv and intermediate larvae. 



wholesale outwash is effected. That something of this nature occurs in many 

 parts of the sea where a continuous yet drifting population is found is suggested 

 by many studies of both the meroplankton and the holoplankton. 



The mystery of how specific planktonic populations can be maintained as 

 such within rather restricted geographical areas is not easy to solve. The 

 answer will most likely be found to include some aspects of water movements 

 correlated with the behavior and life history of the animals. Semi-closed 



